Gun violence is a leading threat to the health and safety of young people in the United States, especially racial minorities in urban areas. Increasingly, public health approaches are being adopted at the community level to combat this problem. The CeaseFire program is an innovative, public health-based strategy found to have significantly reduced shootings in the Chicago neighborhoods where it was implemented. CeaseFire uses community organizations to provide street-level outreach-including referrals to programs and services, modeling of nonviolent conflict resolution skills and direct mediation of disputes-for youth at the highest risk of being a victim or perpetrator of violence. It also uses community mobilization and media campaigns to change social norms about the use of violence. Other cities are attempting to replicate all or some aspects of the CeaseFire model. The street outreach component is thought to most directly reduce violence, but there has been little research on how to do this complex task. An interim evaluation of the program in Baltimore found significant program effects on reducing homicides in a neighborhood where the program was implemented with a high degree of fidelity to the model, but no evidence of benefits in a neighborhood where it was not implemented as the program was designed. Prior research has focused on outcome evaluation, but has not included in-depth study of implementation. This qualitative, multiple-case study will describe and analyze the implementation of the CeaseFire model in Baltimore and Boston, with a focus on the street outreach work component (Aim 1). This study will identify and explain which outreach strategies have been adopted and why-particularly those found to be most effective for preventing shootings (Aims 2 and 3). It will examine and explain how to successfully hire, train, manage and support a staff of street outreach workers (Aim 4). Additionally, this study will test hypotheses about the how program structure, degree of focus on mental health needs and services, outreach worker background, weapon availability and overall level of violence in the city contribute to program success (Aim 5). Data will be collected through in-depth interviews with program staff and by gathering relevant documents, such as reports of mediated conflicts. To analyze the data, interview transcripts and other documents will be read by the investigator who will systematically identify and label ideas and concepts in the text. These labels, called codes, will be refined as new concepts emerge from additional interviews. The coded data will be examined for categories, themes and patterns across data sources and across cases that address the research aims and hypotheses. Numerous cities are planning to add street outreach work to their violence prevention efforts. The findings from this study will inform efforts to expand the program in Baltimore, Boston and other cities by providing practice-based evidence for how the model is best implemented. PUBLIC HEALTH RELEVANCE: This dissertation will address the CDC's Health Protection Goal of Healthy People in Healthy Places, specifically targeting objective 42, "to prevent injuries and violence and their consequences in communities," and 43, "to improve social determinants of health among communities with excess risk." The CeaseFire model, particularly the street outreach worker component, has the potential to be an evidence-based way to reduce violence in the most dangerous and socially disadvantaged communities, but it is necessary to understand exactly how it is best implemented so that it can replicated effectively. By identifying and analyzing the specific tactics that street outreach workers in varied settings use to prevent violence and the organizational practices that foster success, the findings from this study can inform efforts to implement effective street outreach worker programs, thereby reducing shootings and fatalities.